This invention relates generally to a system to automatically refill a liquid from a bulk container to a smaller receiving container without contamination. More specifically, it relates to a system providing fresh liquid dopant chemicals through an automatic refill to a bubbler ampule in a liquid dopant temperature controller that supplies a dopant saturated carrier gas to a diffusion furnace.
Liquid dopant temperature controllers have been utilized in the semiconductor and fiber optics industries to supply dopant chemicals in carrier gases that are saturated with the dopant as a function of the bubbler ampule's, or dopant receiving container's, temperature. The dopant chemicals are ultra high purity liquid chemicals required for these industries.
The ampules in liquid temperature controllers, commonly called bubblers, must be periodically replaced based on the usage of the ultra high purity dopant chemical. The amount of dopant chemical used is a function of the degree of saturation of the carrier gas carrying the dopant chemical to the diffusion furnace and the quantity of carrier gas used. This, in turn, is a direct function of the bubbler ampule temperature. Typical inert carrier gases are nitrogen, argon, or helium. Some typical dopant chemicals utilized in bubblers are 1,1-trichloroethane (TCA), tetraethylorthosilicate (TEOS), and phosphorous oxychloride (POCl.sub.3).
In the past, when the dopant chemical in the bubbler ampule was depleted, typically the ampule had to be removed from the temperature controller and refilled at a remote site. An attempt to create a commercial system to refill the ampules within the temperature controller was developed by the J. C. Schumacher Company and called the CRS chemical refill system. This system refills empty quartz bubbler ampules batchwise in the temperature controllers.
In the typical semiconductor prior art process, a replacement bubbler ampule, with fresh dopant chemical, is inserted into the liquid temperature controller. This replacement of the dopant chemical, however, requires physical removal of the depleted ampule from the liquid dopant temperature controller and suffers from the inability to operate both the diffusion furnace and the liquid dopant temperature controller for a period of time. The temperature of the replacement liquid dopant chemical is lower than that required for operation by this prior art replacement procedure. Normally the furnace tube temperature is then lowered during these periods of non-operation. Prior to recommencing use of the replenished dopant chemicals, both the bubbler ampule and the diffusion furnace have to be reheated to their operating temperatures. Further, test samples are routinely run through the process to ensure that the replenished chemical is not contaminated prior to resuming the production operation. The total liquid dopant chemical replacement process can take from two to eight hours, depending upon the chemical involved and the end use.
In the prior art Schumacher chemical refill system, the same problem was present with the low temperature of the replacement dopant chemical and resultant inability to operate the diffusion furnace until the chemical was reheated. This system had the additional disadvantage of being oversized for use in clean rooms.
Automatic liquid replacement or refill systems for liquids have been utilized in other industries generally where the purity requirements are far less stringent. Generally, however, these replacement systems have been based upon measuring the weight and the receiving container at comparative points in time or by using a time filling sequence to ensure the proper volumetric quantity is delivered. None of the systems were designed to work with the stringent requirements needed for ultra high purity chemicals in the semiconductor industry.
These problems are solved in the design of the present automatic refill system to automatically refill the bubbler ampule in a liquid dopant temperature controller without removing the ampule from the controller.